Shaped objects from fiber reinforced stampable sheet are well known. Broadly, stampable sheet is a composite obtained by a laminating process wherein a reinforcing fiber mat and or layer of thermoplastic resin are pressed together at temperatures above thermoplastic melt. In the stamping operation, the stampable sheet is deformed under pressure at temperatures below thermoplastic melt to form a shaped object.
A major problem associated with the laminating process is in obtaining smooth surfaces from the forming process. This is particularly difficult where either high concentrations of glass fiber are utilized or chopped glass fibers are employed. Fiber strands protruding from the surface will roughen the stampable sheet. This poor surface quality in the stampable sheet will be transferred into the finished shaped object. There is a continuing effort by those skilled in the art to enhance the surface characteristics of these finished stamped parts.
A method for improving the surface quality of stampable sheet is to use a resin layer containing short glass fiber or a mineral filler external to a resin layer containing long glass fibers. This method and variations thereof are disclosed in U.S. Pat. Nos. 4,044,188; 4,098,943; 4,145,227; and 4,269,884. The products of these methods suffer in that they contain a layer which does not benefit from the use of long glass fiber.
Another method to improve surface quality is the use of a fabric surface veil positioned between an external layer of resin and an internal layer of resin containing long glass fibers. This method is disclosed in U.S. Pat. Nos. 4,379,801 and 4,471,018. The products of this method also suffer in that an external layer of resin contains no reinforcing fiber and therefore, the fiber network is not continuous.
It is an object of the present invention to produce a fiber reinforced stampable sheet which has smoother surfaces and which will maintain this smoothness when stamped into finished articles.
It is another object of the present invention to produce a stampable sheet with a reinforcing fiber mat wherein said fibers are internally positioned by the use of a support film.
It is a further object of this invention to provide a fiber reinforced stampable sheet having smooth surfaces wherein the fiber network is continuous and contains long glass fibers.